Composite carbohydrate films



Patented Not-l5, 1938 UNITED STATES PATENT OFFICE No Drawing.Application September 25, 1936, Serial No.-102,600

16 Claims.

The present invention is directed to the pro-. duction of transparentself-sustaining hemi-cellulose sheeting or films preferably carrying onone or both sides of the film a protective coating such as a waterproofcoating. The' naturally occurring vegetable carbohydrate gums areexamples of hemi-celluloses which are eminently suitable for producingfilms of the character set forth. These gums are sometimes looselytermed pentosan gums" in the literature. is clear and accurate asapplied to the gums of the nature of araban, xylan and the like whichyield arablnose and xylose (five carbon sugars) on treatment with diluteacids, it is believed somewhat misdescriptive as applied to naturallyoccurring carbohydrate gums of the nature of galactan and mannan whichyield galactose and mannose by hydrolysis, since mannose and galactoseare six carbon sugars. Mannose and galactose are perhaps more accuratelytermed, therefore, hexosans" and where in this specification the termhexosan is used, a naturally occurring carbohydrate gum, such asgalactan and mannan yielding a six carbon sugar or hexose on hydrolysis,is meant.

The pentosan and. hexosan gums may be obtained from a wide variety ofvegetable life, ineluding many woods, sea weeds, grasses, and otherperennials. Excellent films may be obtained from various bean gums, suchas locust bean, honey locust an, carob bean or seed mesquite, andsimilar beans. The product obtained by extracting the hexosan gumcontent of these beans and similar products is a mixture of hexosans,principally mannan and galactan, the former being present in about 60%and the latter in about 30%. Other hexosans and pentosans may also bepresent. The related pentosans including araban, xylan, and the like ormixtures thereof all produce self-sustaining films.

Self-sustaining films produced from the naturally occurringwater-soluble carbohydrate gums are inherently flexible and moreover,this flexibility is independent of humidity changes. The

' absence of the plasticizlng agent, which is usually hygroscopic, makesthe film produced in accordance with the present inventionnonhygroscopic. Inother words, no plasticizing' agent is necessary torender the gum films sufllciently flexible to be While this term water,Tragasol gum is produced as outlined by H. C. Fuller in The Chemistryand Analysis of Drugs and Medicines. pared at Mallorca, an island offthe coast of Spain. The firm of A. & R. F. Pons of Barcelona are theselling agents. This firm designates the gum as Harina de Endosphermo deSemilla de Algarroba, and their pamphlets set forth the chemical natureof the material as well as its physical properties and industrial uses.When used in the textile art it is sold under the name of Aprestagum".

The Tragasol gums produced by steeping and warm water extraction aretreated as follows: One part of Tragasol on a dry basis is mixed withfrom about forty to sixty parts by weight of water, and the mixture isthoroughly homogenized by any suitable means, as by anexceedinglyrapidly driven impeller blade operating at about 3,000 R. P. M. with a,four inch two blade impeller, the pitch of the blades being from '20 to30 degrees with reference to the'piane of revolution. For larger masses,the R, P. M. will vary so as to maintain an equivalent degree ofagitation. Any other procedure may be employed to produce a readilyflowable plastic. For example, the gelatinous mass may .be passedthrough a standard colloid mill with adjustable plates or poles. As willbe seen from the foregoing treatment no reacting substance is added tothe gum in order to solubilize the same inasmuch as the naturallyoccurring vegetable carbohydrate gums treated in accordance with theinvention, as before stated, are water soluble. They may, therefore, bemade into films in accordance with the process herelnbefore describedwithout chemical change.

This processing preferably'should be carried out so as to reduce theamount of air entrapped to a minimum. However, where a considerableamount of air is entrapped in the form of small bubbles, clarification,while not absolutely necessary, is highly desirable, and suchclarification may be carried out in any suitable manner In order toclarify or deaerate, the plastic mass is placed in a closed vesselequipped'with a slowly moving agitator, whose rate of travel through themass, and the pitch of the blades of which This material is preare suchas to work the mass from the bottom toward the top or upper layer of theplastic. At the same time, the closed vessel is connected with a vacuumpump which removes the air above the plastic, and with the assistance ofthe impeller blades, the plastic is churned, continuously moving theentrapped air bubbles to the surface,

nickel is suitable. faces, non-metallic surfaces may be used, such whilethe space above same is; being continually evacuated by the known meansdescribed above. Within twenty minutes to a half an hour after beingsubjected to this treatment, the mass is completely transparent, and allvisible air bubbles appear to be removed. This treatment and time refersto a depth of plastic approximating ten inches. Greater depths willobviously require somewhat longer time of treatment to procureequivalent results.

The gum plastic is then heated to reduce its viscosity, when suchheating seems to be desirable. The heating step is optional. Whenprocessing locust bean gum, and particularly Tragasol, the plastic isheated to about 60 C. With different gums, the degree of heating willvary, and, therefore, the above specific temperature is illustrative,and not by way of limitation.

The gum plastic is then spread into film or sheeting form and this maybe accomplished by applying the plastic to a clean highly polished inertmetallic surface such as nickel, stainless steel, aluminum and the like.Enduro stainless steel containing 18% of chromium and 8% of Instead ofusing metallic suras polished Bakelite, glass, rubber and equivalentsurfaces. The carrier surface is preferably heated to approximately thetemperature to which the plastic is heated. The plastic is extruded onthe carrier through any suitable extrusion nozzle or other film-formingdevice already in use in the art of manufacturing transparent sheetingfrom cellulose derivatives.

Any smooth polished surface of the character set forth may be coatedwith an agent facilitating the removal of the ultimate sheet. A thinfilm of wax such as carnauba wax, candelilla parafiin and the like issatisfactory. The wax may be applied as a suspension. For example, amixture of carnauba wax 75%, and parafiin wax 25% by weight is suspendedor dispersed in a highly volatile solvent, such as benzol, acetone, orsimilar mixed solvents, preferably using one part by weight of wax toeighty parts of solvent.-

All excess wax should be carefully wiped ofi or a cloudy film willresult. Instead of using waxes, oils may be used, as for example, cottonseed oil, corn oil, olco-stearine, etc. The gum plastic is extruded orpoured onto the carrier surface and gauged down to the desired thicknessby a doctor blade or scraper which moves over strips of such thicknessas will produce an ultimately dried film of the desired dimensions. Thedried film may vary in thickness depending on its specific uses, but asa rule will vary between .001" and 0.003". Under some circumstances, thefilm may be even thinner, and of the order of .0001 of an inch thick.

The carrier surface may be a belt, a wheel or a cylinder or a heavyliquid which is incompatible with the hemi-cellulose plastic such aslocust bean gum, and upon which the latter may be floated. Examples ofsuch liquids are a mercury bath, ortho-di-chlor-benzene,tetra-chlorethane, and the like.

The carrier surface and the gumsheeting is dried in an oven at anelevated temperature, the pressure, preferably, although notnecessarily, being reduced, rapidly moving air passes counter-currentlyto the direction of passage of the film. The temperature of the dryingair may range between 80 to about 150 C. and carry moderate amounts ofhumidity equivalent to 20% to 35% relative when the temperature is lessthan 100 C. If lower temperatures are used, the drying period iscorrespondingly longer. The temperature of drying may vary greatly, solong as the temperature is not sufiicient to char or damage the sheet.The velocity ,of the air may range from 25 to 100 linear feet per minuteover the drying film. It may be stated that the time of drying varieswith the thickness of the film, the temperature and the relativehumidity of the drying air, and the velocity with which the air passesover the drying sheet.

The film is removed from the carrier surface by picking initially, andthen subsequently winding upon a suitable receiving spool. The filmproduced as above may be used as such, but preferably has one or both ofits surfaces coated with a Waterproofing composition to render the filmsubstantially waterproof. The waterproofing compositions may be thoseset forth in applications, Serial Nos. 34,563 and 87,590, saidcompositions including the following classes:

1. Cellulose derivatives such as the cellulose esters and ethersdissolved in their respective solvents, and to which has been added therecognized plasticizing agents for these substances.

2. The various natural and synthetic resins dissolved in their specificsolvents, and plasticized when necessary. 1

3. The oleo resinous varnishes and spirit lacquers. 1

4. Suitable solutions of the various types of natural and syntheticrubbers and rubber derivatives.

5. Thin wax deposits obtained by deposits of these natural and syntheticwaxes or mixtures of same from their suspensions or solutions, or byactually melting and applying such liquids to the surfaces of thissheeting by such known methods as spraying, brush application, printingfrom rolls, fiowing on same, or by immersing or dipping.

One waterproofing coating may be made by preparing the followingcomposition:

' Per cent Cellulose acetate (5 sec. viscosity) '75Ethyl-para-toluene-sulfonamide 25 This may be dissolved in five (5) unitweights of the following solvent to produce the final waterproofingmaterial:

. Per cent Acetone 90 Diacetone alcohol Instead of usingcellulose-acetate lacquer, the following waterproof coatings may beprepared and used:

Per cent 1. Cellulose nitraten 15 Ethyl acetate 40 Di-butyl phthalate 5Butyl acetate 20 Benzol 12 Methanol 8 2. In the above composition, thecellulose nitrate may be subsstituted by a cellulose ether, includingthose specifically hereinbeforc The solvent mixture ,of the above setforth composition may be modified to meet the re quirements of thevarious types of natural resins in order to produce a clear transparentfilm. It will also serve for most of the synthetic resins.

. I Per cent 4. Rubber solutions (solids) '10 Ethylene di-chloride 90.Per cent 5. Waxes 6-10 Solvents 94-90 The solvents or solvent mixtureswill depend upon the particular wax used. For paraflin, solvent naphthamay be used; for Halowaxes or chlorinated naphthalenes, ethylenedichloride may be used; for true waxes such as spermacetti,

carnauba and the like varying mixtures of acetone, ethyl acetate and thelike may be used.

Sheeting similar to that described may be preparedbyextracting thecarbohydrate gum content of various beans by steeping and warm waterextraction, filtering the solution or colloidal mass through a suitablescreen or cloth, and processing as described above. While the bestresults are obtained by extracting locust bean, similar results are alsoprocurable from honey locust bean, the carob bean or seed, the mesquitebean and similar varieties of these species.

If the gum, due to inherent properties or to processing steps, does nothave the property of forming a self-sustaining film, this characteristic.may be imparted to the gum through the addition of small amounts of astarch base having film-forming properties, such as hereinaftermentioned. The starch base may be added in any suitable amount dependingupon the particular gum used. As a general rule, 10% to 30% will besuflicient to render the film continuous and self-sustaining,but'smaller or greater quantities may be used. I j

At this point it'is desired to state that the term starch base includesstarch derivatives and starch degradation products; The termstarch'derivative is intended to cover any prod uct which may beobtained from starch as-a starting point and which contains in itsmolecule a more or less modified form of starch. The term "starchderivative includes such products as starch esters and starch ethers anddextrines. Starch hydrate and partially hydrolyzed starch, which isreally starch itself, responds to the blue iodine test, which appears tobe the criterion to determine the presence of starch. The degradationproducts which may be completely or partially degraded, do not give theblue iodinetest. For example, a degraded product consisting of so-callederythro dextrine gives a red iodine coloration, while totallydextrinized starch gives no color reaction with iodine. Further, on com'plete hydrolysis by acid treatment or with enzymes or bacteria of theproper type, a the oretically one hundred per cent (100%) yield ofdextro-glucose should result.

The term starch hydrate as used in the present specification, covers theproduct which results from the heating of the vegetable starches with. asubstantial amount of water in a nearly neutral solution to the burstingof the granules, and continued heating at substantially the burstgivessatisfactory results.

ing temperature until the plasic mass clarifies. Research work indicatesthat starch'treated as above set forth is the least degraded form ofstarch. The molecular aggregate is very high andgives the characteristicblue iodine test and almost a theoretical yield of glucose.

It is desired to state that when the starch is treated with alkali, suchas caustic soda, in relatively small amounts, as for example, in amountsless than six per cent (6%), the degradation of blue iodine coloration.Practically none of the starch is converted into dextrines or sugars.

While films produced from such mixtures may not be completelytransparent, although in some cases they are, when such films are coatedon one or both sides, they develop a transparency comparable with thatof glass. These films may not be transparent due largely to a slightsurface roughness on the air side, as distinguished from -10 the starchis relatively small, as shown by the a glassy surface produced by thehigh polish of the metal carrier.

As pentosans, hexosans and similar hemi-celluloses are obtainable fromvarious types of pith and many ofthe grasses, sheeting may be preparedtherefrom. In general, the stalks are shredded, boiled with water andallowed to stand. The resulting product is then filtered and treated ashereinbefore described. Certain varieties, however, such as the cerealgrasses, as exemplified by wheat and oats stalks, require long boiling,while others, such as young shrub stalks are allowed to stand in a 3% to5% alkali solution for a suitable length of time. For example, using acaustic soda solution, six (6) hours is sufiicient. The piths from sugarcane stalks and cornstalks, as well as the wood piths, yield to verymuch milder alkali treatment, forming gelatinous masses, which may becoagulated by neutralization with acid, orprecipitated by the additionof alcohol. This precipitation or coagulating operation is done afterthe plastic solution has been given the form of a film.

Sheeting may also be made from beta and gamma cellulose obtainedfromwood. Shredded wood such assaw dust is steeped with an alkali solution,or any solution which will extract the beta and gamma cellulose. Whenusing caustic soda as the steeping agent, a 5% solution usually In somecases, the extraction is facilitated by heating, as for example, to 60to 70 C. This treatment, extracts from the wood the beta and gammacellulose together with a goodly portion of the lignins. Beforefilm-forming, the lignins are neutralized with a suitable acid such asdilute acetic, which throws out the beta cellulose and a portion of thelignins. In treating with acid, it is necessary to use only sufii'cientacid to neutralize the alkali. Excess acid should be avoided as thiswill result in hydrolyzing these carbohydrates into hexose sugars. Assome of these recovered cellulosic products do not of themselves formcontinuous self-sustaining films, it becomes desirable to add thenecessary amount of starch hydrate, gum arabic, or the like, acting asthe vehicle in becoming the desired type of film.

Theremaining lignins are substantially completely removed by a suitablelignin-removing agent, as for example, mild chlorine treatment or bysolvent extraction using alcohol, benzol, turpentine or the like. It isdesired to point out that these films are substantially improved by theadditionof a starch base having filmforming-properties, such as starchhydrate, in a manner above referred to. As the usual thing 10% to 30% ofthe starchbase is sufiflcient to pro-.

duce a continuous self-sustaining film.

The pentosan gums are extractable from a.

wide variety of woods.

The sheeting produced as above set forth from wood gums, may have one orboth sides provided with a waterproof coating.

In my prior Patent No. 2,012,344, reference is madeto the production offilms from pentosan and pentosan' gums, but the basic thought set forththerein involves the addition of plasticizing agents to render the gumfilm flexible to enable it to be used as a packaging or wrappingmaterial. It has now been discovered that broadly transparentself-sustaining films can be produced by merely leaching beans,sea-weeds and the water soluble extracts of certain woods to obtain thenaturally occurring carbohydrate gums, and that self-sustaining filmsmay be made from the so-prepared gums, said films possessing inherentflexibility sufficient to enable the film to be used for packaging. Inother words, no addition product need be added to effect the desired.flexibility. It is desired to point out that the use of a plasticizerrenders the film subject to humidity changes, and without theplasticizer the flexibility of the film is independent of humidity,changes. The tensile strength of these gum films is substantiallygreater than a "starch base film of equivalent thickness. The

films of the preserit'invention when coated with a correctly formulatedlacquer or coating composition, as herein set forth, form a composite''film ofglass-like transparency.

The term "self-sustaining is used to denote a film which is capable ofphysical existence, as

such, without being carried or supported upon gums or mixtures thereofwith a starch base having filmeforming properties may be used to produceself-sustaining'films in accordance with the present invention, saidfilm being provided with a-protective coating on one or both sides, asspecified, to produce a finished composite film of glass-liketransparency. More specifically,

the gum may be selected from water soluble gums, such as arabic,tragacanth, karaya", locust bean, honey locust bean, carob, mesquite,wood gums, pith gums and stalk gums, and then mixed with any one of theother gums or with any two of the other gums, or even with a greaternumber. Such mixtures may have a starch base having film-formingproperties mixed therewith. The starch base may contain a preservativeas pointed out in my application, Serial No.

What I claim is:--

1. A transparent non-hygroscopic self-sustaining thin sheet consistingsubstantially of naturally occurring water-soluble chemically unchangedvegetable carbohydrate gum, said sheet being characterized by theproperty of being inherently' sufficientlyflexible to be used for thewrapping of articles, while being devoid of extraneously addedplasticizer, said flexibility being independent of humidity changes.

2. A transparent non-hygroscopic self-sustaining thin sheet consisting,substantially of gum, said sheet being characterized by the property ofbeing inherently sufficiently flexible to be .used for the wrapping ofarticles, while being devoid of extraneously added plasticizer, saidflexibility being independent of humidity changes.

3. A transparent non-hygroscopic self-sustaining thin sheet consistingsubstantially of naturally occurring water-soluble chemically unchangedcarbohydrate gum coated with a flexible protective film, said sheetbeing characterized by the property of being inherently sufficientlyflexible to be used for the wrapping of articles, while being devoid ofextraneously added plasticizer, said flexibility being independent ofhumidity changes. I

4. A transparent non-hygroscopic self-sustaining thin sheet consistingsubstantially of water-soluble chemically unchanged pentosan gum andcoated with a protective film, said sheet being characterized by theproperty of being inherently sufficiently flexible to be used for thewrapping of articles, while being devoid of extraneously addedplasticizer, said flexibility being independent of humidity changes.

5. The herein described packaging material consisting of a transparentself-sustaining thin sheet consisting substantially of Tragasol gum,said sheet being characterized by the property of being inherentlysufficiently flexible to be used for the wrapping of articles, whilebeing devoid of extraneously added plasticizer, said flexibility beingindependent of humidity changes.

6. The herein described packaging material consisting of a transparentself-sustaining thin sheet consisting'substantially of naturallyoccurring water-soluble chemically unchanged hexosan gum coated with aflexible protective cellulosic film, said sheet being characterized bythe property of being inherently sufiiciently flexible to be used forthe wrapping of articles, while being devoid of extraneously addedplasticizer, said flexibility being independent of humidity changes.

7. The process of producing a transparent sheeting comprising .digestinga material containing water soluble hexosan gums with water free fromsubstances capable of reacting with the hexosan gums in the ratio ofabout 40 to 60 parts of water to one ofsolid material, to form acolloidal mass therefrom, agitating the mass to. increase the plasticityand convert the mass into a flowable plastic, casting the plastic insheet form upon a casting surface, allowing the sheet to solidiiv. andthereafter removing the self-sustaining sheet from the casting surface.

8. The process of producing a transparent sheeting comprising digestinga material containing water soluble hexosan gums with water free fromsubstances capable of reacting with the hexosan gums to form a colloidalmass therefrom, agitating the mass to increase theplasticity and convertthe mass into a fiowable plastic, removing entrapped air bubblestherefrom, casting the deaerated plastic in sheet form upon a castingsurface,removing the excess water therefrom, and thereafter removing theself-sustaining sheet from the casting surface.

9. The process of producing transparent sheeting comprising digesting amaterial containing water soluble hexosan gums with water free fromsubstances capable of reacting with the hexosan gums to form a masstherefrom, agitating the mass to increase the plasticity and convert thesame into a fiowable plastic, removing entrapped air bubbles therefrom,heating the deaerated plastic, casting the so-treated plastic in sheetform upon a casting surface, removing theexcess water' therefrom, andthereafter removing the self-sustaming sheet from the casting surface.-

1 0. The process of producing a transparent 5 sheeting comprisingdigesting a material containing water soluble hexosan gums with waterfree from substances capable or reacting with the hexosan gums in theratio of about 40 to 60 parts of water to one of solid material, to forma colloidal 1 mass therefrom, agitating the mass to increase theplasticity, and convert the same into a flowable plastic, removingentrapped gases therefrom,

heating the so-treated plastic, casting the plastic in film form upon acasting surface, removing the 15 excess water, and thereafter removingthe selfsustaining film from the casting surface.

11. A transparent self-sustaining thin sheet consisting substantially ofhexosan gum typified by locust bean gum, said sheet being coated with aflexible protective film and characterized by the property of beinginherently suificiently flexible to be used for the wrapping ofarticles, while being devoid of extraneous added plasticizer, saidflexibility being independent of humidity changes.

herently sui flciently flexible to be used for the 12. A transparentself-sustaining thin sheet traneously added plasticizer, saidflexibility being independent of humidity changes.

14. A transparent self-sustaining thin sheet consisting substantially ofwater-soluble chemically unchanged naturally occurring hexosan gum andcoated with 'a protective'fllm, said sheet being characterized by theproperty of being inherently sufllciently flexible to be'used for thewrapping of articles while being devoid of extraneously addedplasticizer, said flexibility being independent of humidity changes.

. wrapping of articles, while being devoid of ex- 15. A transparentself-sustaining thin sheet consisting substantially of a mixtureofwatersoluble chemically unchanged pentosan gum and naturally occurringhexosan gum and coated with a protective film, said sheet beingcharacterized. by the property ofheing inherently sufliciently flexibleto be used for the wrapping of articles while being devoid ofextraneously added plasticizer, said flexibility being independent ofhumidity changes.-

16. The process of producing transparent sheeting comprising digesting amaterial containing water soluble naturally occurring vegetablecarbohydrate gum with water free from substances capable of reactingwith the gums in the ratio of about 40 to60 parts water free fromsubstances capable of reacting with the gums to one of solid material toform a colloidal mass therefrom, agitating the mass to increase theplasticity, and convert the same into a flowable plastic, removingentrapped gases therefrom, heating the so-treated plastic, casting theplastic in 'fllm form upon a casting surface, removing the excess water,and thereafter removing the self-sustaining film from the castingsurface.

' HAROLD A. LEVEY.

